Doctor

A doctor (abbreviated as "Dr.") is a person who holds a doctorate and is usually trained in the medical profession, although not always. One exception is Jeffrey Swaim, who adopted the name Doctor Blockhead despite the fact he was not actually a doctor in anything other than his alias. (TXF: "Humbug") The word doctor is also a verb, that can be defined as "to tamper with something". The word was used in this context by Fox Mulder in 1993 and by Dana Scully in 1996. (TXF: "Ice", "Unruhe")

"Young at Heart", "The Post-Modern Prometheus" and "Essence" all include reference to Frankenstein, Doctor Zaius is twice mentioned in "War of the Coprophages", and Doctor Jekyll is referenced in "Underneath", as well as Jekyll's alter ego, Mr. Hyde.

It is unclear if Dr. Death is a fictional character within the X-Files Universe, or if Doggett created the name to describe Dr. Preijers. It is likely Doggett was referring to Harold Shipman, a serial killer the media named Dr. Death.